The present invention pertains generally to lasers and more particularly to nonresonant Raman shifting of laser signals.
Recent developments in rare gas halide lasers such as reported in Appl. Phys. Lett. 29, 707, (1976) and Appl. Optics, 16, 1792, (1977) have resulted in substantial output powers in the uv spectral region. Although the photochemical applications from the generation of uv light at 248 nm and 193 nm (from KrF and ArF lasers respectively) have been numerous, it is desirable for general photochemical applications to have a greater selection of uv wavelengths available with reasonable conversion efficiency.
The technique of Raman shifting has been theoretically shown and experimentally proven as disclosed in the following articles: "Effective Stimulated Scattering in the Ultraviolet and Dispersion of Gain in the 1.062-0.26.mu. Band" by S. A. Akhmanov et al., JETP Lett. 15, 185 (1972) wherein Raman scattering was demonstrated in liquid N.sub.2 from excitation radiation of a stable fourth harmonic of a neodymium laser, "Investigation of Stimulated Raman Scattering and Gaseous Excited by Fourth Harmonic of Neodymium Laser Radiation" by G. V. Venkin et al. appearing in Sov. J. Quant. Electron., 5, 1348 (1972), where results are given of an experimental investigation of stimulated Raman scattering in gaseous hydrogen and deuterium excited by a fourth neodymium laser harmonic. Additionally, an article entitled "Statistical Phenomena in Raman Scattering Stimulated by a Broad Band Pump" by S. A. Akhmanov et al, Sov. Phys. JETP, 39, 249 (1974), discloses the results of a theoretical and experimental investigation of stimulated scattering in liquid N.sub.2 by a broad band pump. Another theoretical description of the Raman scattering processes is disclosed in an article entitled "Simple Theory of Diffuse Vibrational Structure in Continuous uv Spectra of Polyatomic Molecules. 1. Collinear Photodissociation of Symmetric Triatomics" by Russel T. Pack, appearing in the J. of Chem. Phys. 65, 4765, (1976). Although these articles disclose the feasibility of generating numerous wavelengths in the uv spectral region, there is no disclosure of a method or apparatus for enhancing particular Stokes signals to obtain desired wavelengths with reasonable conversion efficiency. Although it is known in the prior art as disclosed in "Energy and Time Characteristics of Stimulated Raman Scattering of Light" by V. A. Zubov et al., Sov. Phys. JETP Vol. 28, p. 231, (1969), that higher power densities within the Raman scattering medium produce a greater number of Stokes signals, this phenomena has not been previously used to enhance any particular Stokes signal, and particularly, not in combination with other parameters which vary the Stokes outputs in a predetermined manner.